Publications by authors named "Sandra Barna"

3 Publications

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Experimental determination of the effective point of measurement of the PTW-31010 ionization chamber in proton and carbon ion beams.

Med Phys 2021 Nov 24. Epub 2021 Nov 24.

MedAustron Ion Therapy Center, Marie Curie-Straße 5, Wiener Neustadt, Austria.

Purpose: The accurate knowledge of the effective point of measurement (P ) is particularly important for measurements in proximity to high dose gradients such as in the distal fall-off of particle beams. For plane-parallel ionization chambers (IC), P is well known and located at the center of the inner surface of the entrance window. For cylindrical ICs, P is shifted from the chamber's center towards the beam source. According to IAEA TRS-398, this shift can be calculated as 0.75·r for light ions with r being the radius of the cavity. For proton beams and in absence of a dose gradient, no shift is recommended. We have experimentally determined P for the 0.125 cc Semiflex IC in both proton and carbon ion beams.

Methods: The first method consisted of simultaneous irradiation of a plane-parallel IC and the Semiflex in a 4 cm wide spread-out Bragg peak. In the second method, a single-energy beam was used and both ICs were positioned successively at the same measurement depths. For both approaches, the shift of the distal edge of the depth ionization distributions recorded by the two chambers at different reference points was used to calculate P of the Semiflex. Both methods were applied in carbon ion beams and only the latter was applied in proton beams.

Results: Both methods yielded a similar P for carbon ions, 0.88·r and 0.84·r , which results in a difference of only 0.1 mm. The difference to the recommended value of 0.75·r is 0.4 and 0.3 mm respectively, which is larger than the positioning uncertainty. In the proton beam, a P of 0.92·r was obtained.

Conclusions: The P for the 0.125 cc Semiflex IC is shifted further from the cavity center as recommended by IAEA TRS-398 for light ions, with the shift for proton beams being even larger than for carbon ion beams. This article is protected by copyright. All rights reserved.
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November 2021

Human Biodistribution and Radiation Dosimetry of the P-Glycoprotein Radiotracer [C]Metoclopramide.

Mol Imaging Biol 2021 04 22;23(2):180-185. Epub 2021 Jan 22.

Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.

Purpose: To assess in healthy volunteers the whole-body distribution and dosimetry of [C]metoclopramide, a new positron emission tomography (PET) tracer to measure P-glycoprotein activity at the blood-brain barrier.

Procedures: Ten healthy volunteers (five women, five men) were intravenously injected with 387 ± 49 MBq of [C]metoclopramide after low dose CT scans and were then imaged by whole-body PET scans from head to upper thigh over approximately 70 min. Ten source organs (brain, thyroid gland, right lung, myocardium, liver, gall bladder, left kidney, red bone marrow, muscle and the contents of the urinary bladder) were manually delineated on whole-body images. Absorbed doses were calculated with QDOSE (ABX-CRO) using the integrated IDAC-Dose 2.1 module.

Results: The majority of the administered dose of [C]metoclopramide was taken up into the liver followed by urinary excretion and, to a smaller extent, biliary excretion of radioactivity. The mean effective dose of [C]metoclopramide was 1.69 ± 0.26 μSv/MBq for female subjects and 1.55 ± 0.07 μSv/MBq for male subjects. The two organs receiving the highest radiation doses were the urinary bladder (10.81 ± 0.23 μGy/MBq and 8.78 ± 0.89 μGy/MBq) and the liver (6.80 ± 0.78 μGy/MBq and 4.91 ± 0.74 μGy/MBq) for female and male subjects, respectively.

Conclusions: [C]Metoclopramide showed predominantly renal excretion, and is safe and well tolerated in healthy adults. The effective dose of [C]metoclopramide was comparable to other C-labeled PET tracers.
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April 2021

Dose Calculations and Dose-Effect Relationships in 177Lu-PSMA I&T Radionuclide Therapy for Metastatic Castration-Resistant Prostate Cancer.

Clin Nucl Med 2020 Sep;45(9):661-667

From the Preclinical Molecular Imaging, AIT Austrian Institute of Technology GmbH, Seibersdorf.

Dose response of 22 patients experiencing mCRPC (metastatic castration-resistant prostate cancer) to Lu-PSMA I&T radionuclide therapy was investigated. Dosimetry calculations are used to assess correlations between dosimetric quantities and biomarker values.

Methods: The patients' age range was 74 ± 7 years at the time of the investigated treatment cycle, and the mean injected activity was 7416 ± 218 MBq. Planar images at several time points postinjection were used for evaluation of absorbed doses to organs and lesion. Ga-PSMA PET/CT follow-up imaging enabled the determination of individual tumor molecular volume (TMV) shrinkage. Changes in 7 different biomarkers after the first treatment cycle were correlated with the calculated absorbed organ and TMV doses, resulting in a total number of 259 investigated correlations.

Results: Sixty-three TMVs were identified in the bone, lymph node, and liver tissue with an average reduction of 32.3%, 84.7%, and 72.9%, respectively. Absorbed doses per unit of administered activity for organs and lesions show good agreement with previous works (0.77, 0.71, and 0.27 mGy/MBq for parotid gland, kidneys, and liver as well as 4.38, 5.47, and 4.95 mGy/MBq for bone, lymph node, and liver malignancies, respectively). Only 37 of 259 possible correlations turned out to be statistically significant, 26 of which are associated with the absorbed dose of an organ and the decrease of alkaline phosphatases.

Conclusions: Although treatment with Lu-PSMA I&T leads to a big reduction of TMV in patients with mCRPC, the lack of correlations calls for studies using voxel-wise dosimetry based on SPECT/CTs.
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September 2020